Method and apparatus for feeding wire to a welding arc

ABSTRACT

A method and apparatus for feeding wire in a welding system include one or more motors disposed adjacent the wire to drive it. A wire feed motor is also disposed along the wire path, and is closer to the source of wire than the torch, and closer to the source than the one or more motors. The motors may be a pair motors disposed on opposite sides of the wire and move the wire to and away from an arc end of a torch. They preferably reversing the direction of the wire within one process cycle. The or more motors may be a stepper motor, a servo motor, a zero backlash motor, a gearless motor, a planetary drive motor, or a linear actuator (such as a piston), in various embodiments.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the art of welding. More specifically, it relates to welding using a short circuit or pulse process.

BACKGROUND OF THE INVENTION

[0002] There are many different arc welding processes used for numerous welding applications. While different processes share some characteristics, such as using an electric arc and/or current flow to provide the heat for the weld, different processes have characteristics that render them desirable for particular applications.

[0003] MIG welding is a widely used process that gives high heat input into the wire electrode and the workpiece, and thus can give high deposition rates. However, the process can be unstable and control of the arc length can be difficult. Also, for some application MIG can be too hot (cause too much heating of the workpiece). The MIG process is often performed as a short circuit or pulse welding.

[0004] Another known welding process is called controlled short circuit welding, or short circuit welding. Short circuit welding is often performed as a MIG process. Generally, short circuit welding includes a short circuit state, wherein the welding wire is touching the weld pool thus creating a short circuit, and an arc state, wherein an arc is formed between the welding wire and the weld pool. During the arc state the wire melts, and during the short circuit state the molten metal is transferred from the end of the wire to the weld puddle.

[0005] Disadvantages of short circuit welding relate to the transitions between states, and instability of the process. Transition from the short circuit state to the arc state was typically caused by providing sufficient current to “pinch” off a droplet. The pinching off at high current can result in a violent disintegration of the molten metal bridge producing excessive weld spatter. Instability also results from the weld pool being pushed away.

[0006] Many attempts in the prior art were made to create a stable short circuit or pulse welding power supply, such as those shown in U.S. Pat. Nos. 4,717,807, 4,835,360, 4,866,247, 4,897,523, 4,954,691, 4,972,064, 5,001,326, 5,003,154, 5,148,001, 5,742,029, 5,961,863, 6,051,810 and 6,160,241, hereby incorporated by reference. These patents generally disclose complicated control schemes that fail to control the process to provide a stable and effective weld. They include control schemes that try to control the deposition of material and/or predict or cause a transition to the subsequent state based on the total energy put into the weld, the length of the stick out, total watts, time of the preceding state, etc.

[0007] These schemes share a common failure: they attempt to control both the energy of the weld and the transition between states using output current or power. This necessarily entails a sacrificing of one control goal (either energy to the weld or state transition) for the sake of the other. The net result is that the control schemes do not perform well at either controlling the energy into the weld or controlling the transition.

[0008] Another short circuit welding control system is disclosed in U.S. Pat. No. 6,326,591. This system adequately controls the energy into the weld, but it does not provide independent control of the transitions between states.

[0009] The present inventors have published descriptions of a controlled short circuit welding process where mechanical movement of the wire (advancing and stopping, slowing or retracting) is used to control the transition between welding states. The short circuit state is entered by advancing the wire until the wire touches the weld pool. The arc state is entered by retracting the wire until the wire does not touch the weld pool, and an arc forms. This system allows a typical output control to be used to control the energy delivered to the weld. By separating control of the transitions from control of energy, the system allows for better control of each.

[0010] A controlled short circuit or pulse welding system requires the capability of advancing and stopping, slowing or retracting the wire. The inventors have disclosed in the literature the use of a stepper motor to control the wire movement. A stepper motor adequately provides for short term advancing and retracting of the wire.

[0011] However, a stepper motor does not necessarily provide adequate feeding of the wire over the long term. Accordingly, a system that provides for advancing and retracting of the wire, and long term feeding of the wire, is desirable.

[0012] One problem with controlled short circuit welding arises when the wire is retracted. The wire from the source is feeding toward the weld, and has momentum in that direction. The retracting motor moves the wire in the opposite direction. With nothing to compensate for the opposing forces, the wire might not feed in a smooth and efficient manner. Accordingly, a controlled short circuit or pulse welder that compensates for the reversal of the wire is desirable.

[0013] Another problem with controlled short circuit or pulse welding is that the prior art has not fully taken advantage of the process control made possible by the mechanical control of the state transitions. Thus, a controlled short circuit or pulse welder that provides for electrical control of the arc for the purpose of controlling heat into the weld, and not for causing transitions from one state to another, is desirable.

[0014] The prior art has not adequately addressed the needs of short circuit or pulse welding at lower currents with thicker wires. The difficult to implement control schemes, in particular, make it difficult to weld with thicker wire, such as 2.4 mm diameter wire, e.g., at low currents, such as less than 100 amps. Accordingly, a controlled short circuit or pulse welding process that may be used at low currents relative to the wire diameter is desirable.

[0015] Pulse welding generally consists of the output current alternating between a background current and a higher peak current. Most of the transfer (of the wire to the weld) occurs during the peak state. Pulse MIG welding systems are also well known. They have variety of power topologies and control schemes that provides the pulse power. Many pulse processes desire a short arc length. However, short arc lengths can result in inadvertent shorting of the wire to the weld pool. Accordingly, a system and method that allows for shorter arc lengths without resulting in an unsatisfactory number of inadvertent shorts.

[0016] Spray transfer is another known process. As in all welding processes, spray transfer is best done with controls that optimize the process. Difficulties with spray processes include controlling the arc length and starting the process. Accordingly, spray transfer with a controlled arc, such as mechanical control, is desired.

SUMMARY OF THE PRESENT INVENTION

[0017] A wire feeder includes a motor that advances, and slows, stops or reverses the wire. It may be used with in a short circuit, pulse or spray process. The wire feeder may be part of a welding system. The wire feeder may have a motor near the torch, reel, or both.

[0018] Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a diagram of a welding system, in accordance with the present invention;

[0020]FIG. 2 is a torch with a buffer and reversible motors in accordance with the present invention;

[0021]FIG. 3 is a cross-sectional view of the torch of FIG. 2;

[0022]FIG. 4 is a detailed cross-sectional view of a buffer in accordance with the present invention;

[0023]FIG. 5 is a cross-sectional view of a weld cable used as part of a buffer in accordance with the present invention;

[0024]FIG. 6 is one wave form of a process cycle in accordance with the preferred embodiment;

[0025]FIG. 7 is one current wave form of a process cycle in accordance with another embodiment; and

[0026]FIG. 8 is graph of the wire feed speed of a process cycle in accordance with one embodiment of the invention.

[0027] Before explaining at least one embodiment of the invention in detail it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. Like reference numerals are used to indicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] While the present invention will be illustrated with reference to a particular welding system using particular components, it should be understood at the outset that the invention may also be implemented with other systems, components, and modules, and be used in other environments.

[0029] Generally, the present invention is a method and apparatus for controlled short circuit or pulse welding that includes mechanical control of transitions between the arc and short circuit states. In various embodiments the process includes a pulse mode or transfer. Control of energy to the weld is effected using the output current or voltage magnitude, wave shape, time, etc. Thus, the transitions are caused to occur by controlling the wire movement, and current can be coordinated with, the transitions to reduce spatter, instability, or other undesirable features, by, for example, changing the current as the transition occurs, or in anticipation of the transition. Alternatives include using the mechanical control described herein with a spray transfer process.

[0030] The mechanical control of the process allows the process to better have a desired arc length. Desired arc length is an arc length, constant or varying, for part or all of the process that helps the process perform better, and may be user set, process set, or controlled. Often, shorter arc lengths will be cooler, and thus may be advantageous for some applications. For example, applications such as welding thinner gauge materials, (auto body, furniture etc.) or pipe welding may be performed with pulse or spray using mechanical control.

[0031] Mechanical control of the states is performed by advancing an slowing, stopping or retracting, or combination thereof, the wire at the arc. Reversing, slowing or stopping the wire causes an arc to form. Advancing the wire causes a short to form. Slowing or stopping the wire causes the arc to form because the wire doesn't advance fast enough to maintain the short while the ball forms. Also, the forward momentum of the ball can cause it to separate from the wire.

[0032] An advance followed by a slowing, stopping or retracting defines one process cycle. (Process cycle, as used herein, includes one cycle of the states of the process such as an arc state followed by a short circuit state, or an arc state, followed by a short circuit state, followed by a pulse state, or it may be defined by current levels—peak, background, peak, background . . . etc.) One process cycle may include multiple speed changes for each current cycle, or multiple current cycles for each speed cycle.

[0033] The advancing and slowing, stopping or retracting (each of which can be called retarding the advancement) are, in the preferred embodiment, accomplished using a pair of motors disposed on either side of the wire, opposite one another and near (or mounted on) the torch. The motors are, in various embodiments stepper motors, servo motors, planetary drive motors, zero backlash motors, dc motors, dc brushless motors, dc direct drive motors gearless motors, or replaced with a linear actuator. The pair is disposed one after the other in one embodiment. A single motor is used in another embodiment.

[0034] Stepper motors are used in the preferred embodiment, and the number, and angle or size of the step is controlled to control the length of wire advanced or retracted.

[0035] Another embodiment provides for a dc direct drive motor (such as a solenoid that moves the drive to and form the wire to directly drive the wire) to reverse, slow, stall or stop (retard) the wire. Other mechanisms, such as clamps, magnetics, induction, linear actuators, etc, are used to reverse, slow, stall or stop the wire in other embodiments. The motor may be a single motor, or two motors, mounted at or near the torch, and may be used with or without a motor at the wire reel. When no motor is used at the reel, a buffer is not always used. Another embodiment provides for a motor (such as one named above) at the reel, and no motor at the torch. Yet another embodiment alters the wire path length in or near the torch, thus “taking up” the wire being fed from the reel. For example, a solenoid in the torch is used to deflect the wire, effectively slowing, stopping or reversing the advancement of the wire to the weld. The motor at the reel can be any motor.

[0036] The preferred embodiment includes a wire feed motor mounted near the source of wire, such as a reel of wire, that drives the wire to the torch (although other embodiments omit this motor). As the reversible motors retract the wire (and the wire feed motor continues to feed the wire) a buffer is provided to account for the increase in wire between the wire feed motor and the reversible motors. Similarly, when the reversible motors advance the wire, wire is withdrawn from the buffer. Controllable motors are used to slow or stop the wire in other embodiments. The reversible or controllable motors move the end of the wire in addition to the movement from the wire feed motor, or they superimpose motion onto motion imposed by the wire feed motor. The speed of the wire feed motor is slaved to the average speed of the reversible or controllable motors, so that, on average, they both drive the same length of wire, in the preferred embodiment.

[0037] The buffer may be anything that stores and returns the extra wire, or provides an increased wire path length between the source and the torch. The buffer of the preferred embodiment includes a wire liner about the wire for at least a portion of the distance from the source to the torch. The liner is disposed in a tube that is wider, and the liner can bend and flex within the tube, thus increasing the length of wire/in a given length of tube. The tube is mounted to a hollow shaft, and the wire passes through the shaft. The shaft is fixed in one position. Thus, as the wire is retracted, the wire moves relative to the tube and shaft (or the tube and shaft may be said to move relative to the wire). The shaft could be mounted to slide along the axis of the wire, and thus move relative to the tip of the torch, thereby increasing the length of the wire path between the tip (arc end) of the torch and the wire source end of the torch.

[0038] Alternatively, the liner may be mounted to the shaft, and the wire moves relative to the liner. The liner is compressible, such as a coil spring, so that as the wire retracts, the spring compresses, in the preferred embodiment. Sensors may be provided that sense the amount of wire in the buffer, or the tension of the wire, and the process controlled (average wire feed speed e.g.) may be controlled in response thereto.

[0039] A controller is provided that causes the motors to retard the movement of the wire (reverse, slow or stop) at least once per process cycle in the preferred embodiment, and controls the current output based on mean arc current (average current during the arc state only, or a function thereof), power, energy, voltage, or other welding output parameters. Feedback may include one or more of short detection, buffer feedback, tension feedback, pool oscillation, in addition to traditional welding parameters. Alternatives include reversing less frequently than once per cycle. One alternative provides for repeated reversals, slowings or stopping during the weld (i.e., not merely at the conclusion of the weld), but not once per cycle. When a pulse process is used to implement the invention each pulse is considered a process cycle.

[0040] For example, braking at the end of the arc cycle can feed forces between wire and droplet, which may disrupt the liquid bridge without retracting action. This is particularly present with lower wire diameters and higher S short circuiting frequencies, but may apply in other circumstances. The droplet has the speed of the wire before braking. This kinetic energy can be enough for disrupting the liquid path. In this case, no retracting is needed, and slowing or stopping is used.

[0041] The control may include controlling heat, penetration and/or bead formation by controlling the advancement of the wire into the weld pool. The relative time in arc state and short state (arc balance) may be set by the user (as may be the time in the pulse state if it is used). Control of parameters such as polarity (balance), gas mixtures etc. may be done in coordination with the relative arc/short times (or other parameters).

[0042] Referring now to FIG. 1, a welding system 100 includes, in accordance with the preferred embodiment, a power supply 102, a wire feeder 104, a controller 106 and a torch 108, and a supply line 112 which feeds welding current, gas, water, control, and current for motors to torch 108, that cooperate to provide welding current on weld cables 105 and 107 to a workpiece 110. Power supply 102, wire feeder 104 and controller 106 may be commercially available welding system components, such as a Miller Invision 456® power supply, and a modified Miller XR® wire feeder. Power supply, as used herein, includes any device capable of supplying welding, plasma cutting, and/or induction heating power including resonant power supplies, quasi-resonant power supplies, etc., as well as control circuitry and other ancillary circuitry associated therewith. Power source, or source of power, as used herein, includes the power circuitry such as rectifiers, switches, transformers, SCRs, etc. that process and provide the output power. Wire feeder, as used herein, includes the motor or mechanism that drives the wire, the mounting for the wire, and controls related thereto, and associated hardware and software. It can include a motor near the source of wire that pushes the wire to the weld, and/or motor(s) near the torch that pulls the wire into the line and to the contact tip, or slows, stops or pulls the wire back from the contact tip. Wire path as used herein, includes the path the wire takes from the wire source to the torch or power supply, and may include through a liner, a buffer, etc.

[0043] Controller 106 is part of wire feeder 104 and power supply 102 in this embodiment. Controller 106 also includes control modules adapted for the present invention, such as a reversible wire feeder control module to control the reversible motors, a mean arc current module, and the control module for the mechanical control of the arc states. Controller, as used herein, includes digital and analog circuitry, discrete or integrated circuitry, microprocessors, DSPs, etc., and software, hardware and firmware, located on one or more boards, used to control a device such as a power supply and/or wire feeder. Control module, as used herein, may be digital or analog, and includes hardware or software, that performs a specified control function. For example, a mean arc current control module controls the output to provide a desired mean arc current.

[0044]FIG. 2 shows torch 108 in more detail. Torch 108 includes, in addition to the features of prior art torches, a pair of motor housing 203 and 205 have motors disposed within to drive the wire to or from the weld, and a buffer 201 to take up wire 209 when it is retracted, and provide wire 209 when it is advanced. Buffer, as used herein, includes components used to take up the wire when the wire direction is reversed and provide wire when the wire is advanced. The end of the wire at the arc is shown as 207. The motor housings and buffer are adjacent to the torch in the preferred embodiment, and near the torch in other embodiments. Adjacent the torch, as used herein, includes abutting, touching or part of the torch, directly or through a housing. Near the torch, as used herein, includes much closer to the torch than the source of wire, such as more than 75% of the way from the source to the torch. One embodiment provides that a handheld torch includes a small spool of wire mounted on the torch.

[0045]FIG. 3 is a cross-sectional view of the torch of FIG. 2, taken along lines A-A. A pair of motors 301 and 302 are preferably stepper motors (although they may be other motors) and drive the wire and are disposed adjacent to the wire, and directly opposite one another, on opposite sides of the wire, thereby substantially equalizing forces on the wire. In alternative embodiments they are disposed one following the other, or on the same side of the wire. Directly opposite one another, as used herein, includes at substantially the same position along a wire path. Disposed adjacent the wire, as used herein, includes being close enough to the wire to push or pull the wire. Drive the wire, as used herein, includes one or both of moving the wire toward the torch and moving the wire away fro0Xm the torch.

[0046] Buffer 201 may also be seen on FIG. 3, and is shown in more detail on FIG. 4, and includes a shaft 401 mounted on a support 403. Shaft 401 has a hollow axis, through which wire 209 passes. Weld cable 105 (FIGS. 1 and 5) is comprised of an outer tube 501 and a liner 503, with wire 209 disposed therein. The outer diameter of line 503 is substantially smaller than the inner diameter of tube 501, to allow for wire length to be taken up or stored by liner 503 flexing within tube 501. Liner 503 is preferably a coil spring that allows for compression and expansion to further buffer the wire. Storing a length of wire, as used herein, includes taking up wire when the wire direction is reversed. Substantially more than an outer diameter of the liner, as used herein includes enough room to move and flex. Wire liner, as used herein, includes a tube in which the wire can easily move. Tube 501 is mounted to shaft 401 so that wire 209 moves with respect to shaft 401.

[0047] A sensor can be included that senses the amount of wire taken up by buffer 201. Examples of such sensors include a wheel with an encoder that is turned as the wire moves past it, or a linear transformer, with the liner being comprised of a ferrite or magnetic material. The controller includes a buffer feedback input that receives the feedback, and provides a wire feed motor output that is responsive to the buffer feedback. Tension in the wire can also be sensed and used to control the process.

[0048] Control of the process from an electrical standpoint is easier since process control is performed using mechanical control of the wire position. Therefore, the welding current becomes an independent process parameter, totally opposite to the conventional MIG process.

[0049] One desirable control scheme uses mean arc current (average current during the arc state, or a function thereof) as the control variable. This allows better control of the melting and heat to the weld, and reduces spatter and instability, compared to prior art control schemes. It is possible to use mean arc current to control the heat, since arc current is not used to cause the transition from arc to short (or the opposite). The control of the states can be coordinated with the current control. For example, if a state transition is to occur at a time T1, the current transition can occur shortly before that, so as to avoid disrupting the weld pool. Another control feature is to allow the user to set relative arc and short time, or balance between EP and EN.

[0050] One desirable arc waveform is shown in FIG. 6, and includes an arc current waveform with three segments—an initial high current segment, an intermediate current segment, and a low current segment. The low current segment is entered into prior to the short forming, thereby enhancing a smooth transition to the short circuit state.

[0051] Another arc waveform is shown in FIG. 7, and is similar to prior art waveforms. The current is increased during the short, and then reduced before the short is cleared and an arc forms. Then, during the arc, a higher current is provided, followed by a gradual current reduction. The current and/or energy during the arc phase, or portions thereof, may be totalized.

[0052] The waveform of FIG. 7 and the prior art such as U.S. Pat. Nos. 4,717,807, 4,835,360, 4,866,247, 4,897,523, 4,954,691, 4,972,064, 5,001,326, 5,003,154, 5,148,001, 5,742,029, 5,961,863, 6,051,810, 6,160,241, and 6,326,591 is combined with the present invention in one embodiment. The prior art teaches to control the process by current control. This embodiment of the present invention replaces the prior process control with mechanical control (slowing, stopping, reversing) but retains the wave form.

[0053] Another embodiment uses the prior art process control, but uses mechanical control (slowing, stopping or reversing the wire) to clear the short (create the arc) if the short fails to clear when expected according to the prior art or if it has not cleared after a period of time. The failure to establish the arc can be determined by monitoring output voltage. This embodiment is particularly helpful to stabilize some of the relatively unstable prior art processes, by providing a “failsafe” transition to the arc state.

[0054] Because the welding current becomes an independent process parameter, the current can be set to the value, which directs the process into the wanted situation by physical determined behavior. For a low spatter material transfer, the forces onto the liquid have to be low, when the cross section of the electrical conductor is low. Therefore, in one embodiment, the currents have to be low during those phases. During the middle part of the short circuit state, where larger cross section of the electrical conductor is present, high forces can be used to move liquids. Also, high currents during the middle part of the short circuit state are possible. During the arc phase, the current can be used for movement of the liquid and determining the melting rate.

[0055] The present invention may be used with known control schemes, but implement them in a more desirable fashion by eliminating the need for current levels to cause transitions. For example, schemes using either arc length or stick-out as a control variable can be implemented easily because the stepper motors allow stick-out to be measured precisely. Because the transitions are caused mechanically, the arc length may be redetermined each process cycle.

[0056] Turning now to FIG. 8, the wire feed speed of a process cycle of the preferred embodiment is shown. Upon detection of a short, as indicated by the voltage dropping below a threshold, the wire feed speed is commanded to be a constant reverse speed. It takes some time for the motor to effect the commanded change. When the reverse wire feed speed is reached, it is held constant. Eventually, the reversing wire forms an arc. The controller continues to command the constant reverse wire feed speed for a length of time that will provide a desired arc length. The desired arc length divided by the wire feed speed will result in the time necessary to continue the constant reverse speed. Thereafter, the wire feed speed is commanded to be the forward wire feed speed. Again, it takes some time for the wire feed speed to reach the commanded forward wire feed speed. The forward speed is held constant until a short is formed.

[0057] In various alternatives, the controller commands a faster or slower wire feed speed in reverse when the open circuit is detected. By commanding a faster reverse speed the desired arc length will be obtained more quickly. Other modifications, such as, other delays, other than constant speeds, changing the commanded speed to forward prior to the desired arc length being obtained to accommodate for the length of time it takes for the motor to bring the wire feed speed back to the commanded forward speed, may be used.

[0058] The present invention may be implemented with a variety of processes, including but not limited to electrode positive, electrode negative, alternating polarity, ac mig, mig brazing, hard facing, and welding with thick wire at low currents. For example, welding on a 2.4 mm wire may be performed at 100 amps, or even 35 or fewer amps with the present invention. Prior art systems required more current on thick wire to cause the short to clear and to enter the arc state. The present invention doesn't rely on current to clear the short, so thick wire and low current may be used.

[0059] The control preferably ties the speed of the wire feed motor to the average speed of the stepper motors, so that the wire feed speed follows the process speed. Averaging speed over 20-30 process cycles (about 500 msec.) provides for effective control.

[0060] Pool oscillation frequency can be found by monitoring the distance the wire travels until a short is created, or an arc is created. One control scheme provides that the state transitions are timed to coincide with the natural frequency of pool oscillation. The controller includes a frequency module and a pool oscillation feedback circuit that effect this control scheme. A short detection feedback circuit may be used as part of the control loop.

[0061] Another embodiment includes implementing mechanical control of the wire in a pulse process. The mechanical control can be used to control arc length and/or help avoid inadvertent shorts. One embodiment provides that the wire be slowed, stopped or reversed during one of the phases of the process, such as during the background current phase, or during the peak current phase. If the wire is slowed or stopped it is less likely to short, and the process can thus be made more stable. Preferably, the mechanical control is linked with the electrical control, so that the stopping occurs on a regular basis. In one embodiment the arc voltage (or other output parameter) is monitored to determine when a short occurs. At that time, the wire is slowed or stopped or reversed. Thus, the short can be prevented, or more quickly cleared, and the process becomes more stable.

[0062] Yet another embodiment includes implementing mechanical control of the wire in a spray process. The mechanical control can be used to control arc length and/or help avoid inadvertent shorts. If the wire is slowed or stopped it is less likely to short, and the process can thus be made more stable. Preferably, the mechanical control is linked with the electrical control, so that the stopping occurs on a regular basis. In one embodiment the arc voltage (or other output parameter) is monitored to determine arc length. The wire is advanced, slowed, stopped or reversed to maintain a desired arc length. Thus, the process can be cooled, and/or, more stable. Other processes such as pulse or short circuit welding can be used with arc length control.

[0063] One application of a combined mechanical-pulse process is used to weld titanium. The combined process runs cooler, and can have a shorter arc, and produce more desirable welds by countering molten surface tension with mechanical control. The combined process can be as described above, wherein mechanical control is added to a pulse process, or it can be performed using distinct mechanically controlled short-arc processes, followed by, preceding or alternated with MIG processes.

[0064] Turning now to FIG. 8, the wire feed speed of a process cycle of the preferred embodiment is shown. Upon detection of a short, as indicated by the voltage dropping below a threshold, the wire feed speed is commanded to be a constant reverse speed. It takes some time for the motor to effect the commanded change. When the reverse wire feed speed is reached, it is held constant. Eventually, the reversing wire forms an arc. The controller continues to command the reverse wire feed speed for a length of time that will provide a desired arc length. The desired arc length divided by the wire feed speed will result in the time necessary to continue the constant reverse speed. Thereafter, the wire feed speed is commanded to be the forward wire feed speed. Again, it takes some time for the wire feed speed to reach the commanded forward wire feed speed. The forward speed is held constant until a short is formed.

[0065] In some alternatives, the controller commands a faster or slower wire feed speed in reverse when the open circuit is detected. By commanding a faster reverse speed the desired arc length will be obtained more quickly. Other modifications, such as, other delays, other than constant speeds, changing the commanded speed to forward prior to the desired arc length being obtained to accommodate for the length of time it takes for the motor to bring the wire feed speed back to the commanded forward speed.

[0066] In various alternatives, the controller commands a faster or slower wire feed speed in reverse when the open circuit is detected. By commanding a faster reverse speed the desired arc length will be obtained more quickly. Other modifications, such as, other delays, other than constant speeds, changing the commanded speed to forward prior to the desired arc length being obtained to accommodate for the length of time it takes for the motor to bring the wire feed speed back to the commanded forward speed, may be used.

[0067] Numerous modifications may be made to the present invention which still fall within the intended scope hereof. Thus, it should be apparent that there has been provided in accordance with the present invention a method and apparatus for controlled short circuit and/or MIG/pulse welding that fully satisfies the objectives and advantages set forth above. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the claims. 

What is claimed is:
 1. A wire feeder for feeding wire from a source of wire in a welding system comprising: at least one stepper motor disposed adjacent the wire and disposed to drive the wire; wire feed motor disposed along a wire path from the source to a welding torch, wherein the torch is closer to the at least one stepper motor than the torch is to the wire feed motor, and wherein the wire feed motor is disposed to contact the wire and move the wire from the source to the torch; and the at least one stepper motor is disposed to retard movement of the wire toward an arc end of the torch.
 2. The wire feeder of claim 1, wherein the at least one stepper motor is disposed to slow the movement of the wire.
 3. The wire feeder of claim 1, wherein the at least one stepper motor is disposed to stop the movement of the wire.
 4. A wire feeder for feeding wire from a source of wire to a weld, comprising a pair of motors disposed on opposite sides of the wire and disposed to move the wire to an arc end of a torch, and to retard movement of the wire to an arc end of the torch.
 5. The wire feeder of claim 4, wherein the pair of motors is disposed to slow the movement of the wire.
 6. The wire feeder of claim 4, wherein the pair of motors is disposed to stop the movement of the wire.
 7. The wire feeder of claim 6, wherein the pair of motors are disposed along a wire path from the source to the torch, adjacent the torch.
 8. The wire feeder of claim 4, wherein the pair of motors are disposed along the wire path closer to the torch than to the source.
 9. The wire feeder of claim 4, further comprising a wire feed motor disposed along the wire path, closer to the source than to the torch, and disposed to contact the wire and move the wire from the source to the torch.
 10. The wire feeder of claim 4, wherein the source includes a reel of wire mounted without a wire feed motor adjacent thereto.
 11. The wire feeder of claim 4, wherein the pair of motors are disposed directly opposite one another.
 12. The wire feeder of claim 7, wherein the pair of motors are stepper motors.
 13. The wire feeder of claim 4, wherein the pair of motors are disposed one after the other.
 14. The wire feeder of claim 4, wherein the pair of motors are servo motors.
 15. The wire feeder of claim 2, wherein the pair of motors are zero backlash motors.
 16. The wire feeder of claim 2, wherein the pair of motors are gearless motors.
 17. The wire feeder of claim 2, wherein the pair of motors are dc motors.
 18. A wire feeder for feeding wire from a source of wire to a weld, comprising: a wire feed motor disposed along a wire path and disposed to contact the wire and move the wire from the source to a torch; and at least one linear actuator disposed adjacent the wire and disposed to retard movement of the wire to an arc end of the torch.
 19. The wire feeder of claim 1, wherein the at least one linear actuator motor is disposed to slow the movement of the wire.
 20. The wire feeder of claim 1, wherein the at least one linear actuator motor is disposed to stop the movement of the wire.
 21. The wire feeder of claim 13, wherein the at least one linear actuator is disposed along the wire path closer to the torch than to the source.
 22. The wire feeder of claim 14, wherein the at least one linear actuator is disposed along the wire path adjacent the torch.
 23. A method of providing wire from a source to a weld in a welding system comprising: driving the wire to a torch with a wire feed motor; and superimposing, onto motion imposed by the wire feed motor, motion of the wire between the wire feed motor and the weld, with at least one stepper motor, wherein the stepper motor retards movement of the wire to the torch, and accelerates movement of the wire to the torch.
 24. The wire feeder of claim 1, wherein the at least one stepper motor is disposed to slow the movement of the wire.
 25. The wire feeder of claim 1, wherein the at least one stepper motor is disposed to stop the movement of the wire.
 26. The method of claim 16, further comprising disposing the at least one stepper motor along a wire path from the source to the torch, and near the torch.
 27. The method of claim 17, further comprising disposing the at least one stepper motor along a wire path from the source to a welding torch, and adjacent the torch.
 28. The method of claim 16, wherein driving the wire includes moving the wire to an arc end of the torch, and retarding the movement of the wire to the arc end of torch.
 29. A method of providing wire from a source to a weld in a welding system comprising driving the wire with a pair of motors disposed on opposite sides of the wire and moving the wire to an arc end of a torch, and retarding movement of the wire to the arc end of the torch.
 30. The wire feeder of claim 1, wherein the pair of motors is disposed to slow the movement of the wire.
 31. The wire feeder of claim 1, wherein the pair of motors is disposed to stop the movement of the wire.
 32. The method of claim 20, further comprising a driving the wire with a wire feed motor disposed closer to the source than to the torch.
 33. A method of providing wire from a source to a weld in a welding system comprising driving the wire to a torch with at least one gearless motor for moving the wire to an arc end of the torch, and retarding movement of the wire to the arc end of the torch.
 34. The method of claim 22, further comprising driving the wire with a wire feed motor disposed along a wire path from the source to a welding torch, closer to the source than to the torch.
 35. A method of providing wire from a source to a weld in a welding system comprising driving the wire to an arc end of a torch with at least one servo motor for moving the wire to the arc end of the torch and retarding movement of the wire to the arc end of the torch.
 36. The method of claim 24 further comprising driving the wire with a wire feed motor disposed along a wire path, closer to the source than to the torch.
 37. A method of providing wire from a source to a weld in a welding system comprising driving the wire to an arc end of a torch with at least one zero backlash motor for moving the wire to the arc end of the torch and retarding movement of the wire to the arc end of the torch.
 38. The method of claim 26, further comprising driving the wire with a wire feed motor disposed along a wire path, closer to the source than to the torch.
 39. A method of providing wire from a source to a weld in a welding system comprising: driving a wire to a torch using a wire feed motor; retarding the movement of the wire to an arc end of a torch with at least one linear actuator.
 40. A method of providing wire from a source to a weld in a welding system comprising driving the wire to, and retarding the movement to an arc end of a torch within one process cycle.
 41. The method of claim 29, wherein retarding includes slowing the movement.
 42. The method of claim 29, wherein retarding includes stopping the movement.
 43. A wire feeder for feeding wire from a source of wire in a welding system comprising: means for feeding wire from the source to a weld; and means for driving the wire to or retarding movement to an arc end of a torch within one process cycle.
 44. The system of claim 30, wherein the means for driving includes at least one stepper motor and a wire feed motor.
 45. The system of claim 30, wherein the means for driving includes at least one servo motor.
 46. The system of claim 32, wherein the means for driving includes at least one planetary drive.
 47. The system of claim 33, wherein the means for driving includes at least one linear actuator.
 48. A wire feeder for feeding wire from a source of wire in a welding system comprising: means for feeding wire from the source to a weld; and means for moving the wire to and retarding movement to an arc end of a torch, disposed on opposite sides of the wire.
 49. A wire feeder for feeding wire from a source of wire in a welding system comprising: at least one dc motor disposed adjacent the wire and near the torch; and wherein the at least one dc motor is disposed to advance the wire toward an arc end of the torch and to retard movement of the wire toward the arc end of the torch.
 50. The wire feeder of claim 36 wherein the dc motor is a direct drive dc motor.
 51. The wire feeder of claim 36 wherein the dc motor is a brushless dc motor.
 52. A method of providing wire from a source to a weld in a welding system comprising driving the wire to a torch with at least one dc motor for moving the wire to an arc end of the torch, and retarding movement of the wire to the arc end of the torch.
 53. A method of providing wire from a source to a weld in a welding system comprising driving the wire to a torch with at least one dc brushless motor for moving the wire to an arc end of the torch, and retarding movement of the wire to the arc end of the torch.
 54. A method of arc welding, comprising: providing pulse welding power to a welding arc; moving wire to the arc, wherein the wire is consumed in the arc; monitoring the arc, to determine when a short occurs; and retarding the motion of the wire in the event a short is detected.
 55. The method of claim 54, wherein retarding is slowing.
 56. The method of claim 54, wherein retarding is stopping.
 57. The method of claim 54, wherein retarding is reversing.
 58. A method of arc welding, comprising: providing pulse welding power to a welding arc, including a peak current phase and a background current phase; moving wire to the arc, wherein the wire is consumed in the arc; retarding the motion of the wire in at least a part of one of at least one of the peak and background phases.
 59. The method of claim 58, wherein retarding is slowing.
 60. The method of claim 58, wherein retarding is stopping.
 61. The method of claim 58, wherein retarding is reversing. 